Vacuum bag - vreća za vakum

Nakon uspjesnog vakumiranja testne sperploce sa fiberglasom, doslo je vrijeme glasirati pravu dasku.
Postoje samo dvije vrste materijala - PVC ili poliuretanska plastika za vakumsku vrecu. Ja sam odabrao vinil, dakle PVC plastiku koju sam imao od prije. Vinil je 1mm debljine i dosta je tvrd, no biti ce dugotrajan!
Trebati ce vam dosta velika plastika. Ovaj vinil je oko 180 sa 120 cm. Preklopljen je po duzoj strani dakle dobio sam 180 sa 60 cm radnu povrsinu tj. vrecu.

Neko sam vrijeme razmisljao kako zalijepiti stranice vrece no previse komplicirati ne vrijedi. Jednostavno sam selotejpom zalijepio dvije strane, a obostranim selotejpom stranu kroz koju sam umetnuo gipsani otisak i dasku.

Prije nego sto vakumiramo potreban nam je neki ventil koji spajamo na vakumsku pumpu. Stari, nevaljni ventil od auto gume i jedan kupaonski ili kuhinjski priljepak za keramicke plocice je dovoljan. Ventil od auto gume sam skratio i izrezao nepotrebnu gumu do pola ventila i skroz do zeljeza.. Kuhinjski priljepak sam probusio te umetnuo dovoljno ljepila i ventil. Gotov ventil na lijevoj strani zgleda ovako:

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After successful test vacuuming  with a wood ply and fiberglass, it's a time to go with a final board. There are two different vacuum bags - PVC or polyurethane plastic bags. I would suggest grab a vinyl sheet from a balcony blinds supplier. I went with a 1mm thickness,  quite tick but strong and paid only $5! You will need a sheet at least 180x120 cm so you can fold it to get 180x60 cm of working vacuum bag.

Some sites suggest gluing with a plastic cement but it's too complicated. I just used a duct tape on two sides and a double sides tape on the entry side of my bag where I've put a plaster mold and my board in.

Before we go with a vacuum we need some kind of valve for connecting a vacuum pump. Old, used auto tires valve and one suction cap for bathroom or kitchen is more than enough. Tyre valve I've cut and removed half of rubber to get to the metal part and on the suction cap drilled a hole (actually cut the top of it - it's got a hole already). Than poured some PVC cement and a valve in a suction cap. Finished valve is on the left side:

Zatim sam probao vakumirati dasku da vidim kako ce se ponasati gipsani otisak, daska i pumpa. Nesto obicne spage na dasku da vakum moze povuci zrak i to je to. Pumpa se palila svakih 30tak sekundi da odrzi vakum na oko 28 in-Hg. Ako tako radi grijati ce se, dakle pazite na pregrijavanje! Sada je sve spremno za glasiranje! Primjetite vrlo vaznu stvar, dasku sam pobrusio grubim papirom po povrsinama koje ce biti lijepljene! Inace bi moglo doci do odljepljivanja slojeva.

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Than I've applied vacuum to see how the plaster mold, board and pump will work. Some cord on top of the board and around the plaster mold to get the air out and that's it. The pump started every 30 seconds or so to keep vacuum on 28 in-Hg. It *will* be a quite hot over 24hrs! Everything is ready now for the fiberglass! Notice important thing, around gluing areas ( ie. foot pads) I've used a medium sand paper, otherwise there might be some de-laminating after glassing.